The present invention relates to an ink jet head, which forms an image by applying ink drops on a recording paper in a predetermined pattern.
As a recording device for forming an image on a recording paper, an ink jet head has hitherto been used. A recording system of the ink jet head includes, for example, a recording system which utilizes thermal energy generated by a heat-generating resistor or deformation of a piezoelectric element in case of ejecting ink drops toward a recording paper, and a recording system which utilizes heat generated with irradiation of electromagnetic wave. Among these recording systems, the recording system, which utilizes thermal energy of the heat-generating resistor, has been attracted special interest recently as a recording system suited to cope with high-density recording because the heat-generating resistor is easily patterned and comparatively large energy can be generated even in case of a heat-generating resistor having a small area.
Such a conventional ink jet head has a structure that a head substrate comprising a base plate, a lot of heat-generating resistors and a pair of electrodes connected to both sides of each of the heat-generating resistors, and a top plate having a lot of ink ejection openings corresponding to each of the heat-generating resistors are disposed on the base plate so as to form a predetermined space between them, and also the space between the head substrate and the top plate is filled with ink. While carrying a recording paper along the outer surface of the top plate, each of the heat-generating resistors is allowed to selectively generate heat based on image data from the outside and air bubbles are generated in ink by means of this heat energy and, at the same time, a portion of ink is ejected outside through each of the ink ejection openings of the top plate. Then, ink is applied at a predetermined position of the recording paper, thereby recording a predetermined image.
A lot of the heat-generating resistors are generally made of an electric resistive material such as Ta2N, TaAl, TaSi or HfB2 and a power pulse to be applied to these heat-generating resistors has a pulse width of 10 to 12 xcexcsec and a power value of 0.33 to 0.40 W.
By the way, it is recently required to eject ink drops outside by quickly generating air bubbles in ink in order to respond to the demand of high-speed recording with a driving cycle of 0.1 msec or less. To meet the demand, it is necessary to allow the heat resistor to generate heat of high temperature (500 to 800xc2x0 C.) in a short time by applying a power pulse having a larger amplitude and a shorter pulse width than that of the prior art (pulse width: 0.5 to 2.0 xcexcsec, power value: 1.60 to 4.10 W) to the heat-generating resistor.
However, in aforementioned conventional ink jet head, since the heat-generating resistor is made of Ta2N or TaAl, the resistance value is drastically reduced because crystallization of the heat-generating resistor arises, when using the ink jet head while repeatedly applying a large power pulse to the heat-generating resistor, thus making it impossible to allow the heat-generating resistor to generate heat at a desired temperature. As a result, scatter in ejection rate of ink drops arises and it becomes impossible to allow ink drops to arrive at a desired position, thereby to cause drawbacks, for example, poor printing such as strain of the image formed on a recording paper.
Because of insufficient mechanical strength, Ta2N and TaAl, which constitute the heat-generating resistor, also had such drawbacks that breakage such as cracking of the heat-generating resistor is caused by the shock of air bubbles collapsing occurred in ink when the heat-generating resistor is allowed to generate heat repeatedly for a long time.
By the way, apart from the ink jet head, a thermal head is known. For example, Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho) No. 154072/1981 discloses that thin-film heat-generating resistors of a thermal head are made of a material consisting essentially of TaxSiyOz. Also Japanese Published Unexamined Patent Application (Kokai Tokkyo Koho) No. 56388/1987 discloses that TiCxe2x80x94SiO2 is used in thin-film heat-generating resistors of a thermal head. However, as described in these Kokai Publications, the thermal head is characterized in that color development of a predetermined portion of a heat-sensitive recording paper is conducted with heating by selectively applying an electric pulse to thin-film heat-generating resistors, said recording paper being contacted to the thermal head. That is, the thermal head is different from the ink jet head each other in a function and a use of their heat-generating resistor, and the ink jet head is required to have a heat-generating head which can be used even under repeatedly applying a power pulse having a larger amplitude and a shorter pulse width than that of a thermal head.
The present invention has been made to overcome drawbacks of a conventional ink jet head and an object thereof is to provide an ink jet head which is capable of recording a good image with less strain and is suited for high-speed recording, and also has a high reliability.
The ink jet head of the present invention comprises a head substrate, a heat-generating resistor and a pair of electrodes, which are attached on the head substrate, and a top plate disposed above the head substrate, the ink jet head being capable of ejecting ink, with which the space between the head substrate and the top plate is filled, through an ink ejection opening by means of heat of the heat-generating resistor,
wherein the heat-generating resistor is made of a silicon oxide material selected from the group consisting of (1) a material consisting of Tax SiOy (provided that x and y meet the expressions: 1.30xe2x89xa6xxe2x89xa61.70 and 1.20xe2x89xa6yxe2x89xa61.95), (2) a material consisting of NbxSiOy (provided that x and y meet the expressions: 1.4xe2x89xa6xxe2x89xa61.9 and 1.4xe2x89xa6yxe2x89xa61.9), (3) a TiCxe2x80x94SiO2 resistive material, a TiC content in the resistive material being set within a range from 55 to 90 mol %, and (4) a Taxe2x80x94Nixe2x80x94SiOx (provided that x meets the expression: 1.2xe2x89xa6xxe2x89xa62.0) resistive material, a tantalum (Ta) content in the resistive material being set within a range from 48 to 70 atomic %, a nickel (Ni) content being set within a range from 0.1 to 2.0 atomic %.
The ink jet head of the present invention includes the following embodiments.
The ink jet head is characterized in that the heat-generating resistor is coated with a protective layer made of an inorganic compound containing at least 0.5 atomic % of oxygens (O).
The ink jet head is characterized in that the protective layer is made of a Sixe2x80x94Oxe2x80x94N inorganic compound.
The ink jet head is characterized in that the oxygen content in the protective layer is gradually increased toward the side of the heat-generating resistor.
The ink jet head is characterized in that a pair of the electrodes are made of aluminum (Al) and contain 0.01 to 0.1 atomic % of silicons (Si) in the vicinity of an interface with the heat-generating resistor.
According to the ink jet head of the present invention,since the heat-generating resistor is made of any material selected from the silicon oxide materials (1) to (4), it is made possible to effectively prevent crystallization of the heat-generating resistor. Therefore, even if a large power pulse is repeatedly applied to the heat-generating resistor in a short time so as to conduct high-speed recording with a driving cycle of 0.1 msec or less, the resistance value of the heat-generating resistor is maintained at a nearly constant value for a long period and, therefore, the heat-generating resistor is always allowed to generate heat at a desired temperature and the ejection rate of ink drops is made uniform, and thus it is made possible to obtain a good image with less strain.
In this case, since the mechanical strength of the heat-generating resistor made of any of aforementioned materials (1) to (4) is increased by markedly reducing a stress accumulated therein, breakage such as cracking of the heat-generating resistor is hardly caused by the shock of air bubbles collapsing occurred in ink even if the heat-generating resistor is allowed to generate heat repeatedly for a long time, and thus the reliability of the ink jet head is improved.
According to the ink jet head of the present invention, since the heat-generating resistor is coated with a protective layer made of an inorganic compound containing at least 0.5 atomic % of oxygens, it is made possible to increase the adhesive strength of the protective layer to the heat-generating resistor by firmly bonding oxygens in the protective layer with silicons in the heat-generating resistor, and to effectively prevent the protective layer from peeling off from the heat-generating resistor due to the shock of air bubbles collapsing occurred in ink.
Furthermore, according to the ink jet head of the present invention, since a lot of oxygens in the protective layer are distributed in the vicinity of the heat resistor by gradually increasing the oxygen content in the protective layer toward the side of the heat-generating resistor, the number of bonds between silicons and oxygens is increased, and thus the adhesive strength of the protective layer is further enhanced.
Furthermore, according to the ink jet head of the present invention, since a pair of aforementioned electrodes are made of aluminum and merely 0.01 to 0.1 atomic % of silicons, which existed in the heat-generating resistor, is diffused in the lower region of these electrodes, silicons are satisfactorily bonded with aluminums in the vicinity of an interface between the heat-generating resistor and a pair of electrodes, and thus a pair of electrodes can be firmly attached to the heat-generating resistor. Therefore, even if the shock of air bubbles collapsing occurred in ink is repeatedly applied to the heat-generating resistor, breakage such as peeling of a pair of electrodes from the heat-generating resistor is effectively prevented.